A magnetic disk drive, which is a disk device, includes a disk-shaped recording medium (that is, a magnetic disk, and a magnetic head that reads/writes information onto the magnetic disk) disposed inside a case or housing. The magnetic head includes, for example, a recording (or write) head and a read head (reading element). The recording head has a main magnetic pole that generates a writing magnetic field. The recording head also includes a writing shield and a side shield, which face each other and are separated from the main magnetic pole by a gap (the writing gap).
In recent years, there is a tendency that the coercivity (or coercive force) of a recording medium increases as the recording density of the disk device becomes higher. As the coercive force of the recording medium increases, a writing magnetic field magnitude required for writing to be performed on the recording medium also increases. Making the writing gap length of the writing head larger is considered as a method for increasing a recording density. However, when the writing gap length is made larger, writing resolution decreases, thereby losing the density. Conversely, the recording density can be improved by making the writing gap length smaller, but in so doing, the magnetic field magnitude decreases. As described above, in order for the recording density of a recording medium to become higher, a larger coercive force is associated with the recording medium. As a result, a decrease in the magnetic field magnitude attributable to the narrowed writing gap of the recording head becomes a problem.